Ferromagnetic material



June 1961 B. T. MATTHIAS FERROMAGNETIC MATERIAL 2 Sheets-Sheet 1 FiledNov. 18, 1958 FIG.

\SUPERCONDUC TING MAGNET/C COMPOSITION OF C ER/UM, GADOL/N/UM AND RU THE N/UM ELECTRIC/ILL) C ONDUC TING C ORE FIG. 3

/NVEN 7-0;? B. 77 MATTH/AS ATTORNEY June 20, 1961 MATTHlAs 2,989,480

FERROMAGNETIC MATERIAL Filed Nov. 18, 1958 2 Sheets-Sheet 2 INVENTOR 8.7. MA T TH/AS A 7' TORNE V United States Patent 2,989,480 FERROMAGNETICMATERIAL Bernd T. Matthias, Berkeley Heights, NJ., assignor to BellTelephone Laboratories, Incorporated, New York, N.Y., a corporation ofNew York Filed Nov. 18, 1958, Ser. No. 774,701 7 Claims. (Cl. 252-625)This invention relates to a ferromagnetic material, and relatesparticularly to a ferromagnetic material which is superconducting at lowtemperatures.

Materials which exhibit the phenomenon of superconductivity at lowtemperature are known in the art. Similarly, ferromagnetic materials arecommon and are found in nature. However, heretofore superconducting andferromagnetic properties have not been found to co-exist in the samematerial to any appreciable degree at the same temperature.

The present invention concerns a composition of matter which is bothferromagnetic and superconducting at the same temperature over anappreciable temperature range. The materials are compositions of cerium,gadolinium, and ruthenium of the general type A13 where A is cerium andgadolinium in certain proportions, and B is ruthenium. Specifically, thecompositions can be represented by the formula where x has a valuebetween 0.10 and 0.01 (inclusive of the end values). Statedequivalently, the compositions are those within a range whose endmembers can be represented by the formulas Particularly usefulcompositions are those in which x in the formula has a value between0.01 and 0.10 inclusive, or between 0.03 and 0.08 inclusive. Thecomposition showing both superconductivity and ferromagnetism at thehighest tem perature has the composition The compositions showusefulness wherever simultaneous magnetic and superconducting propertiesare desirable. For example, the compositions could be used in making thememory elements in a memory matrix of the type described in thecopending application of Umberto F. Gianola, No. 690,478, filed October16, 1957. As therein described, a memory element comprising a length ofconducting wire, for example of copper, silver, gold, et cetera, havinga thin skin of a magnetic metal thereon, is used to store informationalbits. The magnetic skin is treated to have a preset easy direction ofmagnetization (e.g., parallel to the wire axis) by methods such asanhealing the material in a magnetic field. The magnetic skin is thenmagnetized to align portions thereof parallel and/ or antiparallel tothe axis of the conductor. A current passed through the conductor (muchof which passes through the skin) disturbs the magnetic fields set up bythe magnetized skin, and these variations in flux density are read" bydetecting small current pulses generated in other conducting membersaligned in the vicinity of the magnetized conductor. Since the currentsused in the skin-coated conductors to disrupt the magnetization in theskin are small, the attenuation resulting in long wires can become aproblem. The use of a superconducting magnetic skin improves the deviceby reducing attenuation.

In the accompanying drawings:

FIG. 1 is a sectional view of a wire having a magnetic skin ofsuperconducting material thereon;

FIG. 2 is a plot of the temperature, T below which ICC the materials ofthe present invention are superconducting, and the Curie temperature, Tbelow which the materials are ferromagnetic, both plotted as a functionof the composition of the materials;

FIG. 3 is a front elevation, partly in section, of an arc furnaceparticularly suitable for the preparation of the materials hereindescribed.

In FIG. 1 is shown filament 11 of a conducting metal, such as copper,silver, or gold for example, on which there is thin film 12 of asuperconducting magnetic composition of cerium, gadolinium, andruthenium.

In FIG. 2, the units of the ordinate are degrees Kelvin; the units ofthe abscissa are values of x in the formula and x is thus a measure ofthe composition of the material. Curve 13 is a plot of thesuperconducting transition temperature T of the material as a functionof x. Curve 14 is a plot of the Curie point T of the material as afunction of x. In the region below curve 13, the dotted portions ofwhich represent extrapolations, the material will be superconducting. Inthe region below curve 14, the material will be ferromagnetic. In anyregion lying below both curves 13 and 14 the materials will be bothsuperconducting and ferromagnetic. The temperatures at which thematerials will be of interest as both superconductors and asferromagnetic materials are thus those below about 5 degrees Kelvin. Lowtempera tures to within a few fractional parts of a degree from absolutezero can be attained by boiling helium under reduced pressures and usingsupplementary magnetic cooling means known in the art.

In Fig. 3, the arc furnace shown comprises cathode 16, conveniently of arefractory metal such as tungsten, and anode plate 17, of a materialsuch as copper, having depression 18 in its surface. Inlets 19 andoutlets 20 are provided in cathode 16 and anode 17 for circulating coldwater through the electrodes. Cathode 16 is sealed into the chamberformed by cylindrical glass wall 21 and upper and lower cover plates 22and 23 respectively, by bellows 24. Bellows 24 permits movement ofcathode 16 over the area of anode 17. Upper cover plate 22 has entry 25,sealed with a gas-tight seal to plate 22. Sample loading and unloadingis conveniently carried out through entry 25. Other entries (not shown)in cover plate 22 are an inlet and exhaust for gases introduced into thefurnace prior to and during heating. Glass wall 21 is sealed tightly tocover plates 22 and 23 with rubber gaskets 26.

Preparation of the new materials herein described is? convenientlycarried out in an arc furnace of the type described. In such a furnacependant movable cathode 16 isused to strike an arc to water-cooled anode17, usually in the form of a hollow fiat plate. Cooling wateriscirculated over anode and cathode while the arc is active. Shallowdepression 18 in the surface of the anode plate serves to hold themetals being alloyed, present in amounts corresponding to those Wantedin the final composition, and the are is struck to the anode in thevicinity of the reactants, which are fused by the heat of the arc. Topromote complete mixing of the components of the composition, it isuseful to agitate the mixture during heating. This can be doneespecially successfully by mounting the furnace, or at least the anodeportions thereof, in gimbals or an equivalent mounting permitting motionin three perience no unwanted side reactions such as oxidation.. Argonis the gas usually used, but this is a matter of convenience only.

Temperatures in excess of 3500 degrees centigrade can easily begenerated by the arc. Such a temperature is more than sufiicient to fusethe metals cerium, gadolinium, and ruthenium. However, the cooled anodekeeps a thin layer of the materials being fused in a solid condition onthe cold anode surface, so that the melt itself does not ever contactthe metal of the anode. Alloying of the anode and the melt is avoided inthis way.

For operation of a furnace of the type shown in FIG. 3, direct currentof the order of 200 amperes to 300 amperes at 40 volts to 80 volts isrequired. A power unit rated at 400 amperes at 75 volts was convenientlyused in the preparation of the materials herein described. Although thefurnace operates at about 40 volts, it is convenient to have high opencircuit voltage available for starting the are. Heating is carried onuntil fusion of the sample metals is observed. A short additional periodof heating 9 to allow for more thorough mixing of the liquids may beoptionally used.

The preparation of a composition of cerium, gadolinium, and ruthenium ofthe type herein described is given in detail in the following example.

Example A sample mixture consisting of a lump of cerium Weighing 3.042grams (21.7 millimoles), a lump of gadolinium weighing 0.256 gram (1.6millimoles), and a pellet of pressed ruthenium powder weighing 4719grams (46.6 millimoles) was placed in the anode depression of a furnacesuch as shown in FIG. 3. Argon was flushed through the furnace for abouttwo minutes, then a reduced flow of argon was kept passing through thefurnace by restricting the exhaust outlet. An arc was struck between thewatercooled electrodes. A current of about 200 amperes at 40 voltsliquefied the sample metals in about 10 seconds. The are was kept on forabout seconds, then cut off and the melted sample allowed to solidifyand cool. The sample was then inverted in the anode depression bymanipulation through the furnace entry, and the system once more flushedwith argon before another are was struck, as before. After 30 seconds ofheating, the melt was again cooled and the sample inverted. A thirdheating, similar in detail with the two prior heatings, was then carriedout.

After cooling, the homogeneous sample had a weight of 7.968 grams, ascompared with 8,017 grams of starting materials; The bulk of the loss isdue to evaporation. The final material had a composition correspondingwith the formula.

It is to be understood that materials other than the three separatemetals mentioned in the example could have been used as startingmaterials. For example, solid solutions of GdRu in CeRu can be formed,or solid solutions of Gd in CeRu and so forth, if compounds like CeRuGdRu are available. The physical form of the starting materials is notcritical. Powders, ingots, flakes, and other forms are equally operable.

Measurement of the superconducting and ferromagnetic properties of thesample were measured by suspending the sample in a sealed capsule withina detector coil, which coil is in turn suspended within a larger fieldcoil. Thecircuits' of the detector and field coils have coupledreluctance elements, adjusted when there is no sample in the detectorcoil so that variations in the flux of the field coil caused by openingthe field coil circuit generate currents in the detector coil which arenull-balanced by equal and opposite currents set up in the detectorcircuit by the variable reluctance coupling.

The sample is now'inserted into the detector coil. Variations in thefield flux will induce a current in the detector coil, which contains aballistic galvanometer. As the material is diamagnetic or paramagnetic,the deflections of the galvanometer are in a positive or negative sense,indicating fewer or more flux lines, respectively, passing through thesample and detector coil than passed through the empty detector coilwhen the circuit was null-balanced.

The materials herein described show galvanometer deflections as if theywere diamagnetio-due not to diamag-netismbut to the presence of currentsflowing within the materials. These non-attenuating currents, inducedin' the superconductor and revealing the superconducting properties ofthe materials, cut down the flux lines which can permeate the material,and the material registers as a diamagnetic substance.

That the material is neither diamagnetic nor paramagnetic, butferromagnetic, is detected by subjecting the sample to amagnetizingfield, cutting off the magnetizing field, and moving thesample in the detector coil. Flux lines from the remanent magnetizationof the sample, cutting the wires of the detector coil, induce currentsdetectable on the ballistic galvanometer in the detector coil circuit.

Although specific embodiments of the invention have been shown anddescribed herein, it is to be understood they are but illustrative andnot to be construed as limiting on the scope and'spirit of theinvention.

What is claimed is:

1. A material: consisting essentially of a composition corresponding tothe formula 6. A material as described in claim 1 for which x hasa valuebetween 0.03 and 0.08, inclusive of these values. 7. A material asdescribed in claim 1 for which x has the value 0.06.

References Cited in the file of this patent UNITED STATES PATENTS1,290,010 Hirsch Dec. 31, 1918 1,566,534 Haagn Dec. 22, 1925 1,784,827Elmen Dec. 16, 1930 2,699,518 Cohn -1 Jan. 11, 1955 2,829,973 Jessup etal. Apr. 8, 1958 OTHER REFERENCES D. Schoenberg: Superconductivity,Cambridge University Press, Cambridge, England; 1952.

1. A MATERIAL CONSISTING ESSENTIALLY OF A COMPOSITION CORRESPONDING TO THE FORMULA 